Asalf, B., Gadoury, D. M., Tronsmo, A. M., Seem, R. C., Cadle-Davidson, L., Brewer, M. T., and Stensvand, A. Wintermantel, USDA ARS, Salinas (Virus Decline of Strawberry), the Fungicide Resistance Action Committee (FRAC). The Plant Health Instructor. Do not apply more than 30 oz/acre per year. If fruiting structures are absent on affected sample, individual leaves or leaflets may be incubated in a moist chamber for 24 to 48 hours to induce sporulation. The fungus readily infects living, green leaves in the nursery. UC IPM Pest Management Guidelines: Strawberry Cooperative Extension prohibits discrimination and harassment regardless of age, color, disability, family and marital status, gender identity, national origin, political beliefs, race, religion, sex (including pregnancy), sexual orientation and veteran status. ; Powdery mildew usually covers the upper part of the leaves, but may grow on the undersides as well. How to Identify Powdery Mildew Damage. Flowers, petioles, and fruit also can become infected. Hold one end of the tape and lightly smooth the rest of the tape over the infected leaf surface. Leaves infected with powdery mildew initially have small, white powdery colonies on the … Plants infected with powdery mildew look as if they have been dusted with flour. Jacz. Initiation, development, and survival of cleistothecia of Podosphaera aphanis and their role in the epidemiology of strawberry powdery mildew. Economic loss may result from fruit infection. out by fungicide applications. P. aphanis forms ellipsoidal to barrel-shaped, hyaline conidia in true chains (Heffer et al., 2006). Do not use on new transplants, unrooted cuttings, or water-stressed plants. Choose a site with good sun exposure and minimal shade. F. sp. COMMENTS: Under warm, sunny conditions, fruit bronzing may occur. Santos, B., Blanco, C., Porras, M., Barrau, C., Romero, F. 2002. Phytopathology 100: 246-251. Find more information at the following NC State Extension websites: Publication date: July 24, 2014 Disease is favored in summers in northern production regions in nurseries and high tunnels systems in the south. Leaves infected with powdery mildew initially have small, white powdery colonies on the undersides of leaves. St. Paul, MN. Podosphaera aphanis is an obligate, biotrophic fungus that causes damage to strawberry leaves, flowers, and fruit. A&T State University, in all 100 counties and with the Eastern Band of Cherokee Rain, dew, and overhead irrigation inhibit fun… Powdery mildew is usually not a problem on strawberries in annual production systems. Cleistothecia may act as a viable source of inoculum releasing ascopores to cause initial infections. Apply mined sulfur or insecticidal soap on organically certified strawberries. Infected berries will have a dull sheen and mycelium is visible using a 20 to 30x hand lens. Identification of powdery mildew fungi. The fungus cannot survive in the absence of living host tissue, and therefore the source of inoculum must either overwinter on infected live strawberry leaves or be brought in on transplants. Sphaerotheca macularis), occurs in most areas of the world where strawberries are grown. Koike (emeritus), TriCal Diagnostics, Hollister, M.P. On it are clearly visible specks. Warm temperatures with high humidity in the strawberry canopy favors powdery mildew growth on fruit. Magnification may be required to see this, as powdery mildew on strawberry leaves is not as obvious as on other plants. Ideal conditions for infection are dry leaf surfaces, high relative humidity, and cool to warm air temperatures. Avoid applying when leaf temperature exceeds 90°F. P. aphanis is heterothallic, meaning two compatible mating types are required for sexual reproduction. COMMENTS. This publication printed on: Nov. 28, 2020, NC In severe cases, fruit may become cracked and have a tan to rusty-pink appearance. Not all registered pesticides are listed. Powdery mildew (Podosphaera aphanis) infects strawberry plant leaves, flowers and fruit. COMMENTS: The potential for phytotoxicity has not been fully evaluated. Another thing to remember is that if one type of plant gets it, that particular strain of powdery mildew won’t transfer to the other types of plants. Chasmothecia, dark round structures resulting from sexual fusion (Figure SS-3), contain a single ascus, which contains eight (sometimes six) uninucleate ascospores. Revised: Aug. 19, 2019. This is especially important for protectants such as sulfur. Gubler (emeritus), Plant Pathology, UC Davis, W.M. When conditions are favorable, conidia produced on infected plants are wind dispersed. 2013. Avoid overhead irrigation and excess use of nitrogen. Powdery mildew (Podosphaera aphanis) infects the tissue of strawberry plants and despite the fact that it’s mildew, which we usually associate with wet conditions, this strawberry leaf coating is fostered by dry conditions with moderate humidity and temps between 60-80 F. (15-26 C.). P. aphanis infects leaves, flowers, and fruit.Early foliar infections are characterized by small white patches of … NC State University and NC Growers are encouraged to test product or product mixes for phytotoxicity before field applications to determine safety margins. In some cases, the REI exceeds the PHI. In heterothallic ascomycetes, including P. aphanis, mating occurs only between isolates with the MAT1-1 and MAT1-2 idiomorphs. Maas, J. L. 1998. Cooperative Extension is based at North Carolina's two land-grant institutions, Do not apply more than 1 lb a.i./acre per season. The appendages of the chasmothecia are simple and hypha-like (Gadoury et al. This page describes the symptoms of the fungal disease, its spread and recommended control measures. Monitor the field for the first signs of powdery mildew--leaf distortion and discoloration. Powdery mildew Podosphaera aphanis (syn. To limit the potential for development of resistance do not make more than five applications of strobilurin or anilide fungicides per season. APS Press. N.C. There are no known differences in susceptibility in annual varieties. Spores are wind disseminated and short-lived. A simple method for making a slide to confirm a powdery mildew diagnosis can be conducted using a small piece of clear tape. Do not apply within 3 weeks of an oil application. Conidia typically measure 31.2 μm ± 2.8 × 20.39 μm ± 4.1 (Santos et al., 2002). Early signs of infection include small white patches of powdery fungus growing on the undersides of the leaves. Unlike most fungal pathogens, P. aphanis grows epiphytically on plants, producing hyphae on the lower leaf surface and on the surfaces of flowers and fruit. Signs of powdery mildew may be confused with white waxy residue associated with whitefly eggs.